Web Application Development, Best Practices by Jeff Zhuk ...In JSP, HTML code looks exactly as it would appear in a “.html” file. The JSP interpreter automatically translates into
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Java Servlets serve HTTPThe Hypertext Transfer Protocol (HTTP), like HTML was developed by Tim Berners-Lee and CERN in1989 with the main purpose to transfer arbitrary data, and therefore is not restricted to just text, as its name might suggest.
HTTP is a stateless, connectionless protocolHTTP 1.1 requests– GET, POST, HEAD, PUT, TRACE, DELETE, OPTIONS, CONNECT
Although the HTTP 1.1 spec. contains 7 types of requests, many simple HTTP servers only know the commands “GET”, “POST”, and “HEAD”
HTML forms have (hidden or visible) input fields and the ACTION fieldDefault request method is GET
What is Servlet?A servlet extends functionality of a web server similar to an applet in a browser.
– Servlet is a piece of Java code– Servlet is loaded by a Web server to handle client requests– Servlet’s code stays in memory when the request terminates– Servlet can retain its connection across requests– Servlet can chain a client request to another Servlet (servlet chaining)– Servlets usually:
1) Accept input data2) Run or delegate business logics3) Dynamically generate or just transfer HTML response page
For example, when a browser sends a request to the web server, the server may forward the request to a servlet that can process the request and construct a response, usually an HTML page, that is returned to the browser.
public class AbstractServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//Get HTTP headers, cookies, session and form data from the request //Apply business logic, e.g., user authorization //Fill outgoing "response" to specify the HTTP response //including status code, headers, cookies, session data, // send output HTML page back to a client
public class HelloServlet extends javax.servlet.http.HttpServlet {
public void doGet( HttpServletRequest request, HttpServletResponse response) throws javax.servlet.ServletException, java.io.IOException { String html = ”<HTML>\n" +"<HEAD><TITLE>HTML Title</TITLE></HEAD>\n" +"<BODY>\n" +"<H1> This is just an example</H1>\n" +"</BODY></HTML>";
Servlet Best PracticesNew services can be added run time as new JSPs/ASPs or Java™/.NET classes//serviceName and serviceDetails are to be populated // by servlet doPost() , doGet() or service() methods
Service service = // known or new service(Service) Class.forName(serviceName).newInstance();
String content = service.run(serviceDetails); response.setContentType(“text/html"); // “application/xsl” and etc.response.getWriter().println(content);
XML based Service API allows us to describe any existing and future service <ServiceRequest service=“Mail” action=“get”> <Param><paramName1=…></Param></ServiceRequest>
We can find both Dispatcher and Factory patterns in this example. This approach makes it possible to create a unified API for client – server communications. Any service (including new, unknown design time services) can be requested by a client without code change.
JSP ConceptsJSP, similar to Microsoft ASP Technology, simplifies web design.Web Designers who understand HTML can create most of the page using HTML tags and leave the rest for programmers
• As compared to ASP, JSP is better language for dynamic part– Portable to multiple servers and operating systems• As compared to pure servlets, JSP is more convenient to create HTML– Can use standard tools (e. g., HomeSite, DreamWeaver MX)– Model / view / controller paradigm– JSP programmers still need to know servlet programming
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0Transitional//EN"><HTML><HEAD><TITLE>Simple date with JSP</TITLE></HEAD><BODY>Today’s date is <%= new java.util.Date( ) %>.<P>Regular HTML for rest of on-line store’s Web page</BODY></HTML>
Interrelated JSP pages provide presentation, control, and business processing with scriplets and embedded Java beans encouraging “spaghetti” code in JSP.
• • Standard actions• – In JSP, actions are elements that can create and access• programming language objects and affect output• – JSP spec 1.1 defines standard actions that can be used
to interact with any Bean• • useBean, setProperty, getProperty, include, forward,• param, plugin
• – JSP 1.1 and above supports development of reusable modules called custom actions
• – A custom action is invoked by using a custom tag in a JSP page
MVC Model 2 - Better Separation of Business and Presentation Layers
Client(s)
Web Browser
Http Post/Get
Web Tier
JSPs are
forming
The ViewDatabase
Submit Form
Request
Display Page
Response
Servlet and JSP work together. Servlet and related classes, like Struts Action, control application logic and interact with services while JSP forms the presentation
Create JSP - index.jspRemember what is JSP?– Allows some separation of Java and HTML code• Using JavaBeans as “backend” helpers– JSP scriplets provide access to Java in HTML
Create Servlet – train.ServletExampleRemember what is servlet?– Standard Java class to handle an HTTP request and response– Often mixes Java and HTML code
Web Application Development, Best Practices by Jeff Zhuk, JavaSchool.com
Interrelated JSP pages provide presentation, control, and business processing with scriplets and embedded Java beans encouraging “spaghetti” code in JSP.
Create index.jspWebContent right mouse click – NEW JSP file – index.jsp
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0Transitional//EN"><HTML><HEAD><TITLE>Simple date with JSP</TITLE></HEAD><BODY>Today’s date is <%= new java.util.Date( ) %>.<P>Regular HTML for rest of on-line store’s Web page</BODY></HTML>
• Find the webTrain directory in the Eclipse workspace• Copy the WebContent directory to c:/uop/appsZip the content of the folder (without the folder itself) and
rename the compressed file into “yourName.war”
Email this file to me and I will Copy the file “yourName.war” to the deployment directory, for example, Tomcat/Webapps
Point the Browser to the following URLs to test your application: http://yourServer:8080/yourName/index.jsp
public class AbstractServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//Get HTTP headers, cookies, session and form data from the request //Apply business logic, e.g., user authorization //Fill outgoing "response" to specify the HTTP response //including status code, headers, cookies, session data, // send output HTML page back to a client
Servlet’s Initialization and “web.xml”<?xml version="1.0" encoding="UTF-8"?>... Keep existing code generated by Ecllipse... and add after the <web-app ...... <web-app id="WebApp"> <display-name>yourName</display-name> <context-param> <param-name>dsName</param-name> <param-value>jeffcoTrain</param-value> </context-param>
Deploy Your Application • Make sure that your code was compiled with no read spots• Find the webTrain directory in the Eclipse workspace• Copy build/classes into WebContent/WEB-INFO• Copy the WebContent directory to c:/uop/apps• Zip the content of the folder (without the folder itself) and
rename the compressed file into “yourName.war”• Deploy the file “yourName.war” to the deployment directory,
for example, Tomcat/Webapps
Point the Browser to the following URLs to test your application: http://yourServer:8080/yourName/index.jsp http://yourServer:8080/yourName/ServletExample.do